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United States Patent |
5,028,744
|
Purcell
,   et al.
|
July 2, 1991
|
Digitizer with illuminable working surface
Abstract
Digitizer tablet and digitizer tablet structure having an illuminable
working surface are disclosed. A space between a top translucent layer
having the working surface and a source of light is provided so as to
eliminate or minimize undesirable lighting effects at the working surface.
In the preferred embodiments, the space is an air gap (e.g. 0.060-0.250
inch) immediately adjacent the top translucent layer. The air gap is
formed by transparent optical fibers or solid glass or acrylic rods.
Back-lighted, translucent, back-lightable (without light source) and
surface lighted digitizer tablet embodiments are described.
Inventors:
|
Purcell; Alexander M. (Guilford, CT);
Siefer; David A. (Orange, CT)
|
Assignee:
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Summagraphics Corporation (Seymour, CT)
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Appl. No.:
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463612 |
Filed:
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January 11, 1990 |
Current U.S. Class: |
178/18.11; 362/33; 362/97 |
Intern'l Class: |
G08C 021/00 |
Field of Search: |
178/18,19,20
340/712,716
362/33,97
|
References Cited
U.S. Patent Documents
4206314 | Jun., 1980 | Prugh et al. | 178/19.
|
4654762 | Mar., 1987 | Laverick | 362/97.
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4672153 | Jun., 1987 | Kikuchi | 178/18.
|
Other References
ID: The Intelligent Digitizer Advertisement of Summagraphics Corporation.
|
Primary Examiner: Schreyer; Stafford D.
Attorney, Agent or Firm: Rosen, Dainow & Jacobs
Claims
What is claimed is:
1. A digitizer tablet structure having a working surface which may be
illuminated, comprising:
a light-transmitting layer one surface of which is said working surface;
a position determining structure disposed generally coextensive with said
working surface and which cooperates with an object movable on or adjacent
said working surface when at least one of said position determining
structure and said movable object is energized to generate signals
representative of the position of said movable object with respect to said
working surface;
a substantial space between said position determining structure and said
light-transmitting layer; and
spacer means in said space between said position determining structure and
said light-transmitting layer for spacing said light transmitting layer
from at least said position determining structure, said spacer means being
light transmitting and occupying only a small volume of said space;
said digitizer structure being configured to project light from a source to
said light-transmitting layer through said space to illuminate said
working surface.
2. The digitizer tablet structure of claim 1 wherein said
light-transmitting layer is immediately adjacent said space.
3. The digitizer tablet structure of claim 1 wherein said spacer means
maintains a uniform space height of between about 0.030 inch and about 1.0
inch.
4. The digitizer tablet structure of claim 1 wherein said spacer means
comprises at least one elongated element extending for a substantial
distance in said space generally parallel to said light-transmitting
layer.
5. The digitizer tablet structure of claim 4 wherein said at least one
elongated element has a cylindrical outer surface of a diameter
substantially equal to said height of said space.
6. The digitizer tablet structure of claim 5 wherein said at least one
elongated element is an optical fiber.
7. The digitizer tablet structure of claim 5 wherein said at least one
elongated element is a solid cylindrical rod.
8. The digitizer tablet structure of claim 1 wherein said position
determining structure is substantially light transmitting, and said
digitizer tablet structure is configured to project light to said
light-transmitting element from said source through said position
determining structure.
9. The digitizer tablet structure of claim 8 including said light source
which is disposed on a side of said position-determining structure
opposite said space.
10. The digitizer tablet structure of claim 1 wherein said digitizer
structure is configured to project light from said source to said space
without passing through said position determining structure.
11. The digitizer tablet structure of claim 10 wherein said light source
has a light-projecting portion, said digitizer tablet structure including
said light-projecting portion disposed between said position-determining
structure and said space.
12. The digitizer tablet structure of claim 11 wherein said
light-projecting portion of said light source comprises a thin panel.
13. The digitizer tablet structure of claim 12 wherein said panel is a
fiber optic panel.
14. The digitizer tablet structure of claim 12 wherein said panel is an
electroluminescent panel.
15. The digitizer tablet structure of claim 1 wherein said space is an air
space.
16. A translucent digitizer tablet structure having a working surface which
may be illuminated, comprising:
a light-transmitting layer one surface of which is said working surface;
a substantially light-transmitting position determining structure generally
coextensive with said working surface and which cooperates with an object
movable on or adjacent said working surface when at least one of said
position determining surface and said movable object is energized to
generate signals representative of the position of said movable object
with respect to said working surface;
a substantial space between said position determining structure and said
light-transmitting layer; and
spacer means in said space between said position determining structure and
said light-transmitting layer for spacing said light transmitting layer at
least from said position determining structure, said spacer means being
light transmitting and occupying only a small volume of said space;
said digitizer tablet passing light projected from a side of said
position-determining structure opposite said space to said working surface
through said space to illuminate said working surface.
17. The digitizer tablet structure of claim 16 wherein said
light-transmitting layer is immediately adjacent said space.
18. The digitizer tablet structure of claim 17 wherein said spacer means
maintains a uniform space height of between about 0.030 inch and about 1.0
inch.
19. The digitizer tablet structure of claim 16 including said light source
which is disposed on a side of said position-determining structure
opposite said space.
20. The digitizer tablet structure of claim 16 wherein said spacer means
comprises at least one elongated element having a cylindrical outer
surface of a diameter substantially equal to said height of said space,
said elongated element extending for a substantial distance in said space
substantially parallel to said light-transmitting layer.
21. The digitizer tablet structure of claim 20 wherein said at least one
elongated element is an optical fiber.
22. The digitizer table structure of claim 20 wherein said at least one
elongated element is a solid cylindrical rod.
23. The digitizer tablet of structure of claim 16 wherein said space is an
air space.
24. A digitizer tablet structure having a working surface which may be
illuminated, comprising:
a light-transmitting layer one surface of which is said working surface;
a position determining structure generally coextensive with said working
surface and which cooperates with an object movable on or adjacent said
working surface when at least one of said position determining structure
and said movable object is energized to generate signals representative of
the position of said movable object with respect to said working surface;
a substantial space between said position determining structure and said
light-transmitting layer; and
said digitizer structure being configured to project light from a source
through said space to said light-transmitting layer without passing
through said position determining structure to illuminate said working
surface.
25. The digitizer tablet structure of claim 24 wherein said
light-transmitting layer is immediately adjacent said space.
26. The digitizer tablet structure of claim 24 wherein said light source
has a light-projecting portion, said digitizer tablet structure including
said light projecting portion disposed between said position determining
structure and said space.
27. The digitizer tablet structure of claim 26 wherein said
light-projecting portion of said light source comprises a thin panel.
28. The digitizer tablet structure of claim 27 wherein said panel is a
fiber optic panel.
29. The digitizer tablet structure of claim 27 wherein said panel is an
electroluminescent panel.
30. The digitizer tablet structure of claim 24 wherein said space has a
height of between about 0.030 inch and about 1.0 inch.
31. The digitizer tablet structure of claim 24 including spacer means in
said space for maintaining a given space height, said spacer means being
light-transmitting and occupying only a small volume of said space.
32. The digitizer tablet structure of claim 31 wherein said spacer means
comprises at least one elongated member having a cylindrical outer surface
of a diameter substantially equal to said height of said space, said
elongated member extending for a substantial distance in said space
substantially parallel to said first light-transmitting layer.
33. The digitizer tablet structure of claim 32 wherein said at least one
elongated element is an optical fiber.
34. The digitizer tablet structure of claim 32 wherein said at least one
elongated element is a solid cylindrical rod.
35. The digitizer tablet structure of claim 24 wherein said space is an air
space.
36. The digitizer tablet structure of claim 26 including means for joining
said light-transmitting layer and said light-projecting portion into a
first unit, and means for forming a second unit comprising said position
determining structure, said first unit being structured to fit over and be
usable with said second unit such that said working surface of said first
unit functions as a working surface for position determination thereon in
cooperation with said second unit.
37. The digitizer tablet structure of claim 26 including means for joining
said light-transmitting layer, said light-projecting portion and said
position determining structure into a single unit.
38. The digitizer tablet structure of claim 11 including means for joining
said light-transmitting layer, said spacer means and said light-projecting
portion into a first unit, and means for forming a second unit comprising
said position determining structure, said first unit being structured to
fit over and be usable with said second unit such that said working
surface of said first unit functions as a working surface for position
determination thereon in cooperation with said second unit.
39. The digitizer tablet structure of claim 11 including means for joining
said light-transmitting layer, said spacer means, said light-projecting
portion and said position determining structure into a single unit.
40. The digitizer tablet structure of claim 16 including means for joining
said light-transmitting layer, said spacer means and said position
determining structure into a single unit.
41. The digitizer tablet structure of claim 19 including means for joining
said light-transmitting layer, said spacer means, said position
determining structure and said light source into a single unit.
42. A digitizer tablet structure having a working surface which may be
illuminated, comprising:
a light-transmitting layer one surface of which is said working surface;
a position determining structure generally coextensive with said working
surface and which cooperates with an object movable on or adjacent said
working surface when at least one of said position determining structure
and said movable object is energized to generate signals representative of
the position of said movable object with respect to said working surface;
a substantial space between said position determining structure and said
light-transmitting layer;
means for illuminating said working surface comprising means disposed
between said position-determining structure and said space for projecting
light through said space to said light-transmitting layer to illuminate
said working surface; and
means for joining said light-transmitting layer, said thin panel and said
position determining structure into a single unit.
43. The digitizer tablet structure of claim 42 wherein said means for
projecting light comprises a thin panel.
44. The digitizer tablet structure of claim 43 wherein said panel is a
fiber optic panel.
45. The digitizer tablet structure of claim 43 wherein said panel is an
electroluminescent panel.
46. A tablet-type structure having a first outer generally flat surface
which may function as a working surface and which may be illuminated and a
second opposed outer surface, comprising:
a light-transmitting layer one surface of which is said first outer
surface;
a substantial space adjacent a side of said light-transmitting layer
opposite said first surface;
a thin panel disposed adjacent said space for projecting light through
space and through said light-transmitting layer to illuminate said first
outer surface; and
means for joining said first light-transmitting layer and said panel into a
unit having said first and second opposed outer surfaces.
47. The digitizer tablet structure of claim 46 wherein said panel is a
fiber optic panel.
48. The digitizer tablet structure of claim 46 wherein said panel is an
electroluminescent panel.
Description
BACKGROUND OF THE INVENTION
The invention disclosed in this application relates to digitizer tablets
and tablet structures have a working surface which may be illuminated. For
example, the digitizer tablet may be a back-lighted or "surface-lighted"
digitizer tablet, or the digitizer tablet may be translucent and back
lighted by an external light source such as a light box, or the digitizer
tablet structure may form part of a back-lighted or "surface-lighted"
tablet, etc.
Digitizer tablets and their use are well known. See, for example, BYTE
magazine, January, 1989, pages 162-174. In certain applications,
illumination of the working surface is highly desirable. This is
particularly true of applications that require accurate tracing of
drawings, prints, photographic images such as radiology, etc., and CAD
applications. Frequently such applications require a large tablet, e.g.,
one having a 36.times.48 inch working surface.
An illuminated digitizer working surface may be provided in a number of
ways. For example, digitizer tablet structure including a grid or
equivalent structure which functions as part of the position determining
portion of the digitizer may be back lighted. A back-lightable,
translucent digitizer tablet (including grid structure) is disclosed in
U.S. Pat. No. 4,206,314 (Prugh et al.). A back-lighted digitizer device is
disclosed in co-pending U.S. patent application Ser. No. 07/370,913, of
Siefer and Purcell, filed June 23, 1989, which is assigned to the assignee
of this application. The back-lighted digitizer device disclosed in the
'913 patent application includes a translucent digitizer tablet supported
over a lighting compartment in which are mounted fluorescent lamps for
back lighting the digitizer tablet.
The working surface of a translucent and back-lighted digitizer tablet or
tablet structure may show undesirable lighting effects such as patterns,
lines or spots which may detract from or interfere with use of the
digitizer. One reason is that the light which illuminates the working
surface is projected through the entire digitizer tablet or tablet
structure including the grid or equivalent structure, which, in the case
of electromagnetic digitizers, includes a shield spaced from grid wires of
the grid structure. Another reason, as discovered by the applicants
herein, is that structure causing such undesirable lighting effects
projects images which are focussed at or near the illuminated working
surface.
The Prugh et al. '314 Patent discloses neither the problem of undesirable
lighting effects at the illuminated working surface of a back-lighted or
translucent digitizer tablet, nor a solution.
The Siefer and Purcell '913 application discloses a digitizer tablet
structure which eliminates many undesirable lighting effects of a
back-lighted digitizer device. Specifically, the '913 application
discloses an electromagnetic digitizer tablet comprising a sandwich tablet
structure which diffuses light projected to, and/or defocuses any imaging
of the electromagnetic grid structure on, the top working surface of the
digitizer tablet, so that any such imaging is barely, if at all,
noticeable at a typical user's distance of about 18 inches. Included in
the sandwich structure is a clear or transparent spacer disposed between
the grid structure and the working surface of a translucent top element.
A novel digitizer tablet having a working surface illuminated by light
projected through the working surface but not through the entire tablet or
tablet structure is disclosed in co-pending U.S. patent application Ser.
No. 07/350,042, of Siefer, filed May 10, 1989, which is also owned by the
assignee of this application. The tablet disclosed in the Siefer '042
application, which may be referred to as a "surface-lighted" digitizer
tablet, includes a light source disposed between the position-determining
structure and the top working surface. In that surface-lighted digitizer
tablet, the light which illuminates the top working surface does not pass
through the position-determining structure. Accordingly, the position
determining structure does not cause the undesirable lighting effects
described above for a back-lighted digitizer tablet to appear at the
working surface. The surface-lighted tablet of the Siefer '042 application
includes a clear or transparent spacer between the light source and a
translucent top element, which diffuses light from the light source to
assist in providing an even distribution of light on the working surface.
However, even in the back-lighted digitizer device disclosed in the Siefer
and Purcell '913 application and the surface-lighted digitizer tablet
disclosed in the Siefer '042 application, undesirable lighting effects
such as uneven illumination of the tablet's working surface may occur.
Furthermore, moisture or liquids used during manufacture or use may
accumulate between the clear or transparent spacer and the top translucent
element, which may produce further undesirable lighting effects, such as
dark, bubble-shaped patterns, from ambient light reflected from the
surface, and bright bubble-shaped patterns from light emitted by the light
source through the working surface. Also, pressure applied to the working
surface from a stylus, cursor or a writing instrument or from a user
leaning on the working surface, from heavy objects placed on the working
surface, or from the weight of the tablet elements themselves, may cause
temporary or permanent local deformation of elements of the digitizer
tablet, which may also cause undesirable lighting effects.
There is thus a need to improve the illumination of the working surface of
digitizer tablets and like structures.
SUMMARY OF INVENTION
An object of the invention disclosed herein is to improve the illumination
of the working surface of a digitizer tablet or digitizer tablet
structure, or like structure, e.g., by providing substantially uniform
illumination of the working surface, by eliminating undesirable lighting
effects, etc.
It is another object of the invention to provide such improved illumination
in a back-lighted and/or surface-lighted type of digitizer tablet.
It is another object of the invention to provide a digitizer tablet or
digitizer tablet structure, or like structure, having a working surface
that may be illuminated by back lighting from an external light source, in
which illumination of the working surface is improved.
According to the invention, space is provided in a digitizer tablet or
digitizer tablet structure, or like structure, between the working surface
and a source of light for illuminating the working surface. Preferably,
the space is immediately adjacent a translucent top layer or element
(first light-transmitting layer) whose top surface is the working surface.
Such a space is preferably an air gap, although it may receive other
fluids or a vacuum may be formed in the space. The space acts to defocus
and/or diffuse light passing through the space, and thereby eliminates or
minimizes undesirable lighting effects resulting from one or more of the
causes described herein. The thickness of the space is substantial, and
depends upon optical and non-optical factors. By substantial it is meant
that the space is sufficiently large to achieve one or more of the
functions attributed hereto to the space, e.g. large enough so that
moisture which may normally accumulate in use does not bridge the space.
At the same time, the space should not be unduly large in view of the
overall tablet size, thickness of other tablet layers and components, so
as to adversely affect so-called "threshold proximity" of a probe of the
position-determining portion of the tablet.
For example, an air gap of 0.060 inches adjacent a translucent acrylic top
layer of 0.375 thickness has been found to substantially eliminate or
minimize one or more of the undesirable lighting effects described herein.
However, an air gap or a space of from about 0.030 inch to about 1.0 inch
or larger will result in substantial elimination or minimization of
undesirable lighting effects from one or more of the causes described
herein.
Non-optical factors to be considered in selecting the thickness of the
space include mechanical considerations, e.g., support, rigidity, weight,
etc.; electrical considerations, e.g., shielding requirements in an
electromagnetic type digitizer, proximity threshold of the stylus or
cursor to the working surface, etc.; cost; digitizer tablet size; etc.
For many applications, the top element must be supported other than at its
perimeter. In accordance with the invention such support is provided in
the space b at least one spacer element (spacer means) which does not
introduce substantial undesirable lighting effects. Such spacer elements
in accordance with an embodiment of the invention are preferably
elongated, or have the effect of an elongated spacer, e.g., a series of
smaller spacers, have a cross-sectional area small in comparison to the
area of the working surface, and are optically transmissive transversely
to a longitudinal axis of the respective elongated element. By small, it
is meant that the spacer elements occupy, say less than 10% of the volume
of the space. One or more of such spacer elements are disposed extending
below and adjacent the top element, i.e., the longitudinal axis of the
elongated spacer element or elements is substantially parallel to the
plane of the top layer. Thus, a substantial portion of the space remains
unoccupied by such elements, with small portions occupied by one or more
of these light-transmissive spacer elements.
Preferably, the elongated spacer elements have a cylinddical outer surface,
i.e., they are tubular or rod-like. Cylindrical outer surfaced spacer
elements have the advantage of making line or point contacts with the
under side of the top layer, thereby maximizing the volume of the space
and reducing the area of contact of the top layer with any elements which
may optically be imaged at the working surface, and also avoiding the
possibility of forming small air gaps between a spacer element and the top
layer. Preferably, the cylindrical outer surfaced spacer elements are
substantially non-compressible to minimize contact with the top layer.
In accordance with preferred embodiments, the elongated elements are
conventional, transparent optical fibers or solid transparent rods of
acrylic, glass, etc.
According to one embodiment of the invention, a tablet structure is
provided which includes position determining structure (e.g. a grid
structure), a top (light-transmitting) translucent element or layer, and
an air gap between the position determining structure and the top
translucent layer. Preferably, the air gap is immediately adjacent the top
layer. The tablet structure in one embodiment is substantially translucent
and back-lightable, i.e., a light source (or the tablet structure) may be
disposed so that light is projected to the top layer through the position
determining structure. Such a back-lightable tablet structure may be
provided as a translucent stand-alone digitizer tablet without a light
source, i.e., requiring an external light source, or as part of an
integrated, back-lighted digitizer tablet which includes a light source.
The translucent digitizer tablet (without integrated light source) may be
placed over an external light source as, for example, a light box, light
table or an x-ray illuminating device. When forming part of a back-lighted
digitizer tablet, the digitizer tablet structure may be connected to a
light box device as generally described, for example, in the Siefer and
Purcell '913 application, the disclosure of which is hereby incorporated
herein by reference.
The tablet structure according to another embodiment may form part of a
surface-lighted digitizer tablet, as generally described in the Siefer
'314 application, the disclosure of which is hereby incorporated herein by
reference. In that embodiment, an air gap generally as described above is
formed between the top translucent layer and a light source such as an
electrolumimenscent panel or a fiber optic panel.
The above and other objects, aspects, features and advantages of the
invention will be more readily perceived from the description of the
preferred embodiments thereof taken in conjunction with the accompanying
drawings and appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is illustrated by way of example and not limitation in the
figures of the accompanying drawings in which like references denote the
same or corresponding parts, and in which:
FIG. 1 is a cross section view of a portion of a backlighted digitizer
device similar to the one disclosed in co-pending application Ser. No.
370,913;
FIG. 2 is a schematic cross-section view of the tablet portion of the
digitizer device of FIG. 1 illustrating causes of undesired lighting
effects;
FIG. 3 is a cross-sectional schematic view of a portion of a digitizer
tablet structure incorporating the invention;
FIG. 4 is a cross section view of a portion of a translucent digitizer
tablet, similar to the tablet portion of the device of FIG. 1,
incorporating the invention;
FIG. 5 is an exploded perspective view of the digitizer tablet of FIG. 4;
FIG. 6 is a cross-section view of a portion of the tablet of FIG. 4
including structure for mounting it to light box;
FIG. 7 is a cross section view of a portion of a surface lighted digitizer
tablet incorporating the invention; and
FIG. 8 is a cross-section view of a portion of another embodiment of a
surface-lighted digitizer tablet incorporating the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Although description of the preferred embodiments is made with respect to
digitizer tablets employing electromagnetic technology, the invention is
not limited to such digitizer tablets, and is applicable to digitizers
employing other technologies.
The digitizer device 10 shown in FIG. 1 is an integrated back-lighted
digitizer tablet and light source which is described in detail in
application Ser. No. 370,913. Device 10 comprises a base 12, lighting
compartment 14 and translucent digitizer tablet 16. Fluorescent lamps 18
mounted to base 12 in lighting compartment 14 function as a light source
to project light through translucent digitizer tablet 16 to back light it.
Tablet 16 is hinged at 20 to base 12 so that tablet 16 may be pivoted open
to expose the interior of lighting compartment 14 for servicing, e.g.,
replacement of fluorescent lamps 18. As described in more detail in
application Ser. No. 370,913, device 10 is constructed so that working
surface 24 of translucent top element 26 is illuminated by light from
lamps 18 while undesirable lighting effects are prevented or minimized.
Tablet 16 includes top translucent layer 26, a clear, solid spacer element
28, a transparent printed circuit board (PCB) 30 having grid wires of an
electromagnetic grid structure on opposite sides thereof, a translucent,
solid spacer 35, a perforated grid shield 37 and a clear, solid support
plate 39. The functions of these parts are described briefly below and in
more detail in application Ser. No. 370,912.
Shield 37 is preferably made of sheet aluminum that is thick enough to be
rigid, e.g. 0.05 inch thick. This allows a relatively large number of
holes 43 to be provided in shield 37 so that it is substantially light
transmissive, e.g. 48%, whereby a substantial percentage of the light from
the lamps 20 passes through shield 37.
PCB 30 is a transparent insulating board having fine conducting grid wires
printed on opposed sides thereof.
Spacer element 35, which electrically isolates the grid wires printed on
the lower surface of the PCB 30 from the shield 39, is preferably a
transparent plastic, e.g., acrylic, about 0.2-0.3 inch thick, e.g., 0.22
inch. To reduce weight, a thin-walled spacer (described below) having thin
sheets interconnected by vertical ribs may be used instead of a solid
spacer.
Spacer element 28 mounted between PCB 30 and top layer 26 is a sheet of a
transparent plastic material, such as acrylic, having a thickness of about
0.07 to about 0.09 inch, e.g., 0.08 inch.
Top layer 26 is a translucent plastic material, e.g., translucent acrylic,
and has a thickness of between 3/8 and 1/2 inch, e.g., 3/8 inch.
The portion of tablet 16 above PCB 30 is configured so as to defocus the
shadows cast by the opaque portions of the tablet in the light path from
the lamps 18, and to diffuse the light as widely as possible as it passes
through tablet 16.
Undesirable lighting effects may be produced at working surface 24 as a
result of small spaces or gaps 45 (FIG. 2) between adjacent elements of
tablet 16, or from variations or changes in the thicknesses of elements
26-39 of tablet 16. Such spaces or gaps 45 and thickness variations may be
the result of imperfections or irregularities in the various elements of
tablet 16, e.g., they are not perfectly flat. They may also result from
flexing, sagging, warping or compression of the elements (as at 46) during
assembly or use of tablet 16. For example, the elements be stressed during
use in a number of ways such as from pressing the stylus or cursor against
top element 26, resting heaving objects on top element 26, bending tablet
16, subjecting tablet 16 to adverse environmental conditions, from sagging
of elements 26-39 due to their weight, etc.
For large tablets, e.g., having a working surface of about 36 inches by 48
inches, tablet 16 may sag from its own weight. In such large tablets,
posts 47 are provided inwardly of the tablet perimeter to support tablet
16. Posts 47 are constructed to have optical characteristics as described
in Ser. No. 370,912 (e.g. transmit light in all directions, permit light
to enter and exit easily), and thereby avoid the undesirable lighting
effects described in that patent application. However, posts 47 may
slightly compress or flex elements 26-39 (as at 49) when top element 26 is
pressed with forces typically encountered during use of tablet 16. Flexing
and/or compression of elements 26-39 reduces or eliminates the usual
minute gap (not shown) between the adjacent elements, thereby modifying
the optical properties of tablet 16.
FIG. 2 shows such spaces 45 and flexing, sagging, compression, etc., of
elements 26-29 at 46 and 49 highly exaggerated for clarity and ease of
visual presentation. As also shown in FIG. 2, spaces 45 may simply be air
gaps of varying size in various locations, or they may contain liquid 50,
for example, condensed moisture, or water or other liquids such as
solvents and cleaning fluids which may have not completely dried during
manufacture and ultimately accumulate in gaps 45.
Those air gaps 45 and/or liquid 50, and flexing, compression, etc. of
elements 26-39 may cause undesirable lighting effects at working surface
24, for example, uneven illumination, bright and dark spots and patterns,
etc. Liquid 50 in gaps 45 between elements of tablet 16 tends to produce
various bubble-shaped spots or patterns visible on working surface 24. The
spots and patterns on working surface 24 from liquid 50 appear dark when
the tablet is not back lighted because of non-uniform reflection and/or
refraction of ambient light by the liquid and other parts of tablet 16
resulting from different indices of refraction in adjacent regions. Those
spots or patterns appear bright when the tablet is back lighted because of
the focussing effect of liquid 50.
Similarly, variations in the thickness of air gaps, liquid accumulations,
or in laminating adhesives that are used to bond adjacent elements in a
unitized tablet structure, may produce interference "fringe" or "rainbow"
patterns and other unevenness in the appearance of the working surface 24.
Such variations may occur during manufacture, or may be produced by
stresses, flexing, etc. of the elements while the tablet is in use.
Generally, smaller air gaps tend to produce dark patterns or spots when
surface 24 is not back-lighted, and bright patterns or spots when it is.
While FIGS. 1 and 2 depict a tablet supported by posts 47, tablets
unsupported inwardly of their perimeter and translucent tablets (without
light source) may exhibit one or more of the undesired lighting effects
described herein resulting from one or more of the conditions described
herein.
In accordance with the invention, a tablet structure 60 depicted in FIG. 3
is provided with an intentional air gap 62 adjacent the bottom surface 64
of top translucent layer 26, i.e., on the interior side of translucent
layer 26 opposite working surface 24. Air gap 62 is provided between top
translucent layer 26 and tablet element 66 which, depending upon the
particular tablet embodiment, may be a grid structure, a panel-type light
source, a spacer or support element, etc. The remainder 68 of the
particular tablet is disposed below element 66. Details of such digitizer
tablets have been omitted from FIG. 3 for clarity of presentation.
Specific digitizer tablets employing an intentional air gap 62 in
accordance with the invention are described below.
Intentional air gap 62 is of substantial height and large enough so that
small amounts of condensed moisture which may accumulate during normal use
or small amounts of other liquids not completely dried during manufacture
do not completely fill air gap 62. This ensures that an air gap is
essentially always provided adjacent substantially all of the bottom
surface 64 of translucent layer 26. The presence of air gap 62 along
substantially the entire bottom surface 66 of translucent top layer 26
prevents formation of the small air gaps 45 (FIG. 2) which may otherwise
form in digitizer tablet 16 of FIGS. 1 and 2, thereby avoiding the
accumulation of liquid 50 described above. Additionally, a substantially
continuous air gap 62 tends to minimize the optical effects of
irregularities, imperfections, flexing, etc. of top translucent element
26. Further, air gap 62 performs a diffusing function for light passing
therethrough to provide a more uniform projection of light to top
translucent element 26; and air gap 62 acts to defocus the optical effects
of irregularities, imperfections, flexing, moisture or liquid
accumulations in tablet structure below air gap 62.
The thickness of air gap 62 depends upon optical and non-optical factors.
For example, an air gap of as little as 0.060 inch adjacent a translucent
acrylic top element of 0.375 inch thickness has been found to achieve the
functions described above and substantially eliminate or minimize the
undesirable lighting effects described above. However, an air gap having a
height of from about 0.030 inch to about 1.0 inch or higher will perform
the desired functions and result in substantial elimination or
minimization of undesirable lighting effects from one or more of the
causes described above. The size of the air gap also depends on tablet
size, where the gap may increase to 1 inch or more as the tablet size
increases to several feet or more. The specific digitizer embodiments
described below consider both optical and non-optical factors in setting
air gap 62.
Referring to FIG. 3, air gap 62 is maintained by elongated spacers 70 which
occupy only a small portion of the air gap. (Spacers 70 and air gap 62 are
shown exaggerated in FIG. 3.) Spacers 70 are light transmissive and do not
form dark or bright lines. Spacers 70 preferably transmit light in all
directions and permit light to easily enter, be transmitted through and
exit the respective spacer. In short, spacers 70 should appear optically
not to be present.
It is preferred that spacers 70 be tubular, i.e., have a cylindrical outer
surface, so as to minimize the area of contact between spacers 70 and top
translucent layer 26. For example, such tubular spacers 70 will make line
and/or point contacts (rather than area or surface contacts) with top
translucent layer 26. This avoids the possibility that smaller air gaps,
which may fill with liquid, will be formed between spacers 70 and top
translucent layer 26. It is preferred that spacers 70 be transparent
optical fibers or transparent, solid glass or plastic rods. Of these,
optical fibers are preferred because they provide better light
distribution at working surface 24 than solid rods. Also, optical fibers
may be obtained in small diameters with relatively tight tolerances.
However, whether optical fibers or solid rods are used may depend upon
non-optical factors such as the height of gap 62 desired to satisfy
optical, mechanical, electrical or assembly requirements.
FIGS. 4 and 5 depict a translucent digitizer tablet 80 which incorporates
an air gap 62 in accordance with the present invention. Tablet 80 is
translucent, as is tablet 16 of device 10 in FIG. 1, but does not include
a light source. Rather, tablet 80 may be placed adjacent an external light
source such as a light box, light table or an x-ray illuminating device
(all not shown). Tablet 80 is thus similar to tablet 16, but with an
intentional air gap 62 replacing solid spacer element 28 of tablet 16.
Also, tablet 80 depicted in FIGS. 4 and 5 includes a channeled spacer
sheet 35a instead of the solid spacer 35 of tablet 16 depicted in FIGS. 1
and 2.
Air gap 62 in tablet 80 is provided by optical fibers 70a supporting top
translucent layer 26 (FIGS. 3 and 4). Optical fibers 70a are conventional,
and are commercially available from Mitsubishi Rayon Company Ltd. under
the commercial designation ESKA. Preferably, the diameter of fibers 70a
for use in tablet 80, which is of relatively large size, is 0.060 inch.
They are spaced about 2 inches apart, and a plurality are used. Other
diameter fibers may be used, but that diameter is preferred for the
present construction of tablet 80. Fibers 70a extend adjacent bottom
surface 64 of top layer 26 and each thus occupies about 3% of the air gap
volume between adjacent fibers. Fibers 70a have a circular outer surface
that provides point or line contact with the translucent element 26, and
resist compression, so as to minimize the area of the contact with the
translucent top layer 26 with fibers 70a, as described above. Optical
fibers 70a are preferably applied to the PCB 32 over a transparent layer
of double-sided acrylic adhesive tape 82. Fibers 70a are laid in position
by a jig (not shown) so that they are parallel to the y-axis of the
tablet, with their centers spaced about 2 inches apart. The double-sided
acrylic adhesive tape 82 hardens after fibers 70a are in place, so as to
provide a permanent bond between the PCB 30 and one side of the fibers
70a. This maintains the spacing between the fibers 70a to ensure that
adequate support is provided to maintain a uniform air gap 62 between the
translucent top layer 26 and PCB 30.
Alternatively, solid glass or acrylic rods of suitable diameter may be
utilized.
Tablet 80 thus includes top translucent layer 26, PCB 30, and shield 37,
which for purposes of the invention may be identical or nearly identical
to the corresponding elements of tablet 16. As mentioned above, spacer 35a
is a channeled member, but could be identical to solid spacer 35 of tablet
16. Translucent bottom support 39a may be made of the same transparent
acrylic material as support 39 of tablet 16, but is thicker (e.g. 0.625 to
1.0 inch) because tablet 80 is a self-contained unit and requires more
rigidity and support than tablet 16 which is hinged to lighting
compartment 14.
The height of air gap 62 between the translucent top layer 26 and PCB 30 is
selected as described above to be large enough to help defocus images
projected from lower layers, and to prevent liquid from locally bridging
the distance between the translucent top layer 26 and PCB 30, which would
otherwise compromise been found that the use of tubular spacers 70a to
maintain this particular air gap between the translucent top layer 26
(0.375 thickness) and an underlying element prevents the spotted
appearance described above, without sacrificing the defocusing and
diffusing effects previously provided by a solid spacer 28, and without
producing line images on working surface 24.
Tablet 80 is also different from tablet 10 in that the translucent top
layer 26 is held against fibers 70a by an acrylic frame 86 that is solvent
bonded to bottom surface 64 of element 26 along the perimeter thereof. The
sides of tablet 80 are protected from mechanical damage and the shield 37
is electrically insulated by a semi-circular flexible bumper 88 fixed to
ABS plastic frame 86. Screws 90 fasten base 39a to frame 86, which with
top layer adhered to frame 86, produces a sandwich structure holding the
various elements together.
As mentioned above, in the embodiment shown in FIGS. 4 and 5, a rigid,
square-channeled sheet of extruded TWIN-WALL plastic sheet 35a is used in
place of the solid sheet 35 shown in FIGS. 1 and 2. This extruded sheet is
particularly advantageous since tablet 80 is used independently as a
self-contained digitizer tablet. For example, tablet 80 may be placed over
a light source such as a conventional light box or x-ray displayer.
Alternatively, tablet 80 and/or such light sources may be modified so that
tablet 80 may conveniently be used with such light sources.
Thus, tablet 80 because of its structural stability permits it to be used
without additional rim or housing structures. Tablet 80 is a highly
compact, streamlined unit that can be placed directly on existing lighted
surfaces, making it a convenient unit for use in retrofitting existing
light tables and boxes and X-ray displays. Thus, translucent tablet 80 is
portable and can be used as a removable, optional accessory for such light
devices. Clips, pins, etc., and other structure may be employed to fasten
the tablet to such existing light devices.
If desired, a control module (not shown) containing amplifiers and position
direction circuitry may be provided externally of tablet 80, and to which
a stylus and/or cursor may be connected. This reduces the thickness and
complexity of tablet 80. Such control modules are currently in use on
back-lighted digitizer tablets of the assignee of this application. Thus,
the control module reduces the bulk of the tablet 80 without sacrificing
accuracy or software compatibility. In particular, such a control module
provides the local signal processing that is needed for noise immunity, as
well as for accurate signal detection and interpretation. The control
module also provides a standardized computer interface communication
controller so that the coordinate valves and other probe signals provided
by tablet 80 may be input directly to a computer and storage devices via a
standard modem.
Referring next to FIG. 6, tablet 80a is similar to tablet 80, except that
it includes structure for hinging it to a light compartment 14 in
generally the same way as tablet 16 is fastened to lighting compartment
14. Such structure includes a flanged portion 92 of the lighting
compartment sidewall 94 on which an edge 93 of tablet 80a rests. A
plurality of screws 90 fasten the edge of tablet 80a to flanged portion
90. Element 39a may be thinner since tablet 80a is fixed to light
compartment 14, i.e., element 39a may be replaced by element 39 of FIGS. 1
and 2.
Referring next to FIG. 7, a surface lighted digitizer tablet 100 which
incorporates the present invention is depicted. Digitizer tablet 100 is
similar to the surface lighted digitizer tablet described in application
Ser. No. 350,042, except that intentional air gap 62b, between light panel
102 and top translucent element 26b, replaces a solid transparent element.
Air gap 62b is provided by at least one transparent acrylic spacer rod 72b
having a diameter of 0.250 inch. As indicated above, rods 72b of other
diameters may be utilized. Alternatively, fiber optic spacers 72a of
appropriate diameter may be utilized. Rods 72b may be adhered to top
translucent layer 26b as described above for tablet 80. Light panel 102
may be an electroluminescent panel, or a fiber optic panel, connected to a
light source 103 as described in application Ser. No. 350,042.
Thus, as described above and in application Ser. No. 350,042, tablet 100
depicted in FIG. 7 includes a translucent acrylic top layer 26b of about
5/16 inch thickness, a 0.250 inch thick air gap 62b, 0.250 inch diameter
acrylic spacer rods 72b, fiber optic panel 102 of about 3/32 inch
thickness, a panel support 104 in the form of a transparent sheet of
acrylic of 1/16 inch thickness, and conventional tablet structure
referenced generally 106. Tablet 100 may be assembled using adhesives to
form a rigid tablet.
FIG. 8 depicts a presently preferred embodiment of a surface-lighted
digitizer tablet 100c having a 17 inch.times.24 inch active area
incorporating the present invention. Tablet 100c comprises: a translucent
acrylic top element 26c of 0.250 inch thickness; an air gap 62c of 0.250
inch thickness provided by two transparent acrylic spacer rods 72c of
0.250 inch diameter spaced about 6 inches apart; an acrylic fiber optic
light panel 102c of 0.250 inch thickness commercially available in the
form of a woven optical fiber panel from Lumitex Inc.; a PCB 30 which may
be similar or identical to that described above, a flexible foamed plastic
element 110 of 0.220 inch thickness to insulate and space PCB 30, and a
base 112 of a laminated honeycomb material e.g. NORCOR, of 0.625 inch
thickness. Base 112 is rigid to provide support for tablet 100c. A foamed
plastic 110 is provided weight reduction and to accommodate variations in
the surface of PCB 30. Foam 110C acts as a spacer to accommodate fiber
optic panel 102C. A honeycomb structure is provided for base 112 because
such structures are relatively rigid yet relatively lightweight. The
foregoing components are held together by an extruded plastic frame 114
and a mounting bracket 116. Bracket 116 is screwed to base 112 and is
engaged in slot 118 of frame 114. Frame 114 and top element 26c have
mating shoulders 119,120 which engage when screw 122 is tightened to base
112. Another bracket 124 and screws 125 secure top layer 26 to frame 114.
An opaque rigid "block out" sheet of ABS plastic occupies gap 62 outside
the active area of the tablet. Part 88C, similar to bumper 88, and frame
86C, similar to frame 86, are secured together and to block out sheet 126.
Thus, bracket 116 and frame 114 when fastened together interlock the
various digitizer elements together to form a unitized tablet structure.
If desired, various elements of tablet 100c may be fastened, bonded or
laminated together by known techniques.
Certain changes and modifications of the embodiments of the invention
herein disclosed will be readily apparent to those of skill in the art.
Moreover, uses of the invention other than in digitizer tablets will also
be readily apparent to those of skill in the art. For example, the
invention is not limited to digitizer tablets that are back or surface
lighted, as light for illuminating the tablet working surface may be
supplied by means other than those disclosed herein. Spaces other than air
gaps may be provided, and they may be formed in ways other than those
described herein, and they may be positioned in areas of a tablet
structure other than those specifically illustrated. Also, the various
layers and elements may be adhered in sandwich or luminations other than
as described herein. It is the applicants' intention to cover by the
claims all such uses and all those changes and modifications which could
be made to the embodiments of the invention herein chosen for the purposes
of disclosure which do not depart from the spirit and scope of the
invention.
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